Electrical apparatus



Dec. 6; 1938. C, MCNEIL 2,139,599

ELECTRICAL APPARATUSV Filed Oct. 1, 1955 INVENTOR.

Char/es [../Wc /Ve/7 Patented Dec. 6, 19938 UNITED STATES ELECTRICAL APPARATUS Charles I. McNeil, Bloomfield, N. J., assignor to Eclipse Aviation Corporation, East Orange, N. J., a. corporation of New Jersey Application October 1, 1935, Serial No. 43,106

1 Claim.

This invention relates to dynamo electric machines, and particularly to variably loaded dynamo electric machines of the type having an inherently high accelerating capacity such as di- 5 rect current motors with armature and field winding in series. v I

An object of the invention is to provide a novel method of controlling the potential across the terminals of a direct current motor, the control )n being such as to minimize the breakaway shock by reducing the initial torque and consequent initial acceleration, but without interfering with the ability of the motor to thereafter accelerate suiiiciently to reach a speed commensurate with l5 the torque to be exerted, and then maintain such high speed with a minimum current consump tion.

Another object is to provide novel electrical means for effecting the above described control 20 without the use of relays or switches other than the necessary starting and stopping switch.

These and other objects of the `invention will become apparent from 'inspection of the followin g specification when read with reference to the if, accompanying drawing wherein isillustrated the preferred embodiment of the invention. It is to be expressly understood, however, that the drawing is for the purpose of illustration only, and is not designed as a definition of the limits of the 1, invention, reference being had to the appended claim for thisv purpose.

In the drawing:

Fig. 1 shows schematically al system of electrical connections embodying the invention, and

2.'. Fig. 2 shows a second embodiment. y

My novel method of control involves, first, the provision of a resistor 6, having a zero (or practically zero) temperature resistance co-eiiicient, and a second resistor of high temperature reo sistance co-eicient, ythe latter (shown at 1 in Figs. 1 and 2) to be inserted in shunt relationship to the amature windings A and in series relationship to the first named resistor 6. The shunt connection may be of either the long 45 shunt" character, as indicated in Fig. 1, (that is,

PATENT OFFICE in shunt with the series field` I0 as well as the armature) or the short shunt character, as indicated in Fig. 2. With veither arrangement the operation is as follows:

Assuming the armatureA to be mechanically 5 connected to a part to be driven, such as an engine crankshaft, whose inertia places a heavy load upon the armature at the moment of breakaway, closure of switch 8 will result in a characteristically heavy-draw of current from source lo 9. The high initial current through the cold high resistance coefficient resistor 1, together with the high initial armature current causes a large drop in resistance 6 and consequently a low voltage gradient from point 4 to point 5. 'This low pol5 tential difference between points 4 and 5, occurring as it does during the initial breakaway period in the operation, when the voltage is usually relatively high, causes the motor to accelerate less rapidly than would otherwise be the case,

and as aresult of the reduced acceleration the breakaway shock is' correspondingly lessened.

As the work of driving the load proceeds the continued rise in temperature in the resistor l lowers the current consumption correspondingly, and since the armature current consumption is further reduced in accordance with the law of operation of series wound motors (lower current as speed rises) the motor is free to attain, and subsequently maintain, its maximum speed (for the load imposed) without any substantially greater draw of current from source 9 than would normally occur in a motor of this type, and of course the voltage drop across resistor 6 becomes a minimum as the current consumption drops to U the lower value.

What is claimed is:

The combination with a direct current motor having armature and field windings in series, of a pair of resistors distinct from said eld windings, said resistors having decidedly difierent reactions to temperature variations, one of said resistors being in series with the armaturewinding and the other in shunt.

CHARLES I. MCNEIL. 

